Philip Reeve doesn't do man-made fabrics and comes over rather squeamish at the thought of plastic. "I wouldn't dismiss modernity completely, but I'm not very interested in anything post-1946," he says. "I think the 'stuff' was better in the past - the trains, the clothes, the machines - everything had more character then. Modern technology doesn't appeal to me but a great big steam engine does."

It's this love of history and its "stuff", wittily wrapped up in an SF disguise, that propels A Darkling Plain, the winner of the 2006 Guardian children's fiction prize and the concluding volume of an outstanding quartet which began with Mortal Engines, an adventure set after the Sixty Minute War has destroyed 21st-century civilisation.

In this future world, which reads more like an alternative history than science fiction, the prevailing ideology is Municipal Darwinism: moveable cities, towering up layer upon layer of living and working space, roam around a familiar but altered landscape known as the Great Hunting Ground, with the larger ones preying on the smaller.

Partly inspired by the massive road-building programme of the 90s, which allowed roads and then housing to eat up the countryside, Reeve embarked on Mortal Engines without any thought of it being specifically a children's book, though it was exactly the kind of "big and rambling" book he would have enjoyed himself as a teenager. It has a huge cast of Dickensian characters, including teenager Tom Natsworthy, a Third Class Apprentice with a naive and hopeful attitude, who blunders into danger accompanied by Hester Shaw, a vengeful assassin with whom he teams up in the Out-Country. The ride is a fast one and full of the unexpected. Reeve seems effortlessly able to whisk up entirely credible cities with ladders and walkways, unfurling sails and dangling ropes, as well as complicated dramas with cascading subplots. Saving it all from the weightiness that this might imply is Reeve's humour in his word play on names of characters and places, and his sly contemporary references - "goggle-screens" which people gather round in shop windows; the circular archaeological discovery known as a "seedy"; and rumours of a mysterious piece of ancient technology known as an "eye-pod". The series is marked out from the rash of lesser fantasies by Reeve's strong dislike of some of the key traditions of the genre. "Anything with a prophecy, I instantly want to stop reading. It irritates me in fantasy that everyone is black or white and you know how they will end up." Instead, many of Reeve's characters have an uncertain status and may behave villainously or virtuously on different occasions.

Mortal Engines was planned as a one-off, but then there was Predator's Gold and Infernal Devices. In this concluding volume, A Darkling Plain, Tom Natsworthy is middle aged; the skirmishing between traction cities has been replaced by an all-out struggle between the Green Storm and the Traction League, with the threat of the bomb created by the Ancients always lurking in the background. It's a bigger, bolder and more serious novel than Mortal Engines with some great set-piece battles which Reeve always approaches from interesting sideways perspectives. It also has a clever twist, a circular ending, which Reeve says he had feared would be corny but is, in fact, delightfully satisfying.

A Darkling Plain fulfils Reeve's intentions as a writer precisely. He believes that the primary purpose of reading is escapism and dislikes books that have a message. "If it's to be interesting it has to raise questions but, equally, if it's going to be interesting it has not to give answers."

Reeve trained as an illustrator but quickly decided that he wasn't good enough to make a real go of it and never even hawked his portfolio of Rackhamesque pictures around on finishing his course. Much later, his first published work was as an illustrator creating the visual side of Terry Deary's Horrible Histories. But, alongside the illustration, since childhood he has written stories, plays and films. He was influenced by his childhood reading of Rosemary Sutcliff and Tolkien, and his adult reading of Dickens, whose works he rereads regularly and regards as "the model of what a proper novel is. Within the space of a page, he can make you laugh and cry and be completely surprised". Much of his inspiration comes from his passion for films: he credits Star Wars (which took him off into reading Asimov and Bradbury) and John Boorman's Excalibur, which led him into the Arthurian stories and on to Malory's retellings, as the two defining experiences.

All of this, coupled with a love of the Goon Show and The Hitchhiker's Guide to the Galaxy, feeds into his writing, creating something that is not old-fashioned at all, but an irresistible new universe just waiting to be explored.